1. Field of the Invention
The present invention relates to an image detection apparatus and an image forming apparatus.
2. Description of the Related Art
Conventionally, an image detection apparatus is known which optically detects a correction chart in which many patches having different colors and densities are arranged for the purpose of correcting the color or the like characteristics of an image forming apparatus.
This image detection apparatus may be incorporated in the image forming apparatus as an internal unit to perform its functionality, or may be another device connected to the body of the image forming apparatus.
For example, Japanese Patent Published Application No. 2008-8967 discloses a color image forming apparatus having a capability of correcting color characteristics. In the case of this color image forming apparatus, since there is a difference between the front and back sides of a sheet in the degree of correction, different correction charts are provide respectively for the opposite sides in order to generate the correction data in accordance with the fixing history of the sheet. Also, in the case where the correction chart for front side and the correction chart for back side are formed to overlap in the plane of paper, i.e., where color patches for back side is formed just in back of color patches for front side with the sheet material therebetween, the information of the image (color patches) in the back side can be included in the information detected by a color sensor. Because of this, there is a problem that the correction accuracy may be degraded. In order to deal with this problem, this color image forming apparatus is structured to form correction charts on the front and back sides of a sheet respectively in such positions as not to overlap each other. When detecting the correction chart on the back side after detecting the correction chart on the front side, the color sensor is shifted to avoid overlapping. Each correction chart described in Japanese Patent Published Application No. 2008-8967 consists of a plurality of patches which are linearly arranged as a patch array in the direction of conveying sheets.
In accordance with the technique described in this publication, however, only two patch arrays are detected for the front and back sides respectively. In addition to this, since the patch array formed on the front side is of the same type as the patch array formed on the back side, it actually means that only one patch array is effectively detected. So far, high picture quality is required of image forming apparatuses, and thereby it is important to detect a number of color patches corresponding to several hundreds through 1600 colors and the like. However, in the case where such a very large number of color patches are linearly formed, a large number of sheets have to be used and uselessly discarded, resulting in an unfavorable situation.
Taking into consideration the above circumstances, it is an object of the present invention therefore to provide an image detection apparatus and an image forming apparatus which can colorimetrically measure an appropriate number of patches while inhibiting unnecessary sheet discharging.